Retroviruses utilize cellular tRNA molecules as primers for reverse transcription of viral RNA into double stranded DNA. In avian retroviruses, tRNATrp is used as the primer for reverse transcription and is selectively packaged into virions. Preliminary results indicate that avian tryptophanyl-tRNA synthetase (TrpRS) is selectively packaged into Rous sarcoma virus (RSV) virions. This project will further explore protein-tRNA and protein-protein interactions that aid in the selective packaging of tRNATrp in avian retroviruses; specifically, the interaction between avian Gag and human TrpRS in the presence and absence of tRNATrp. These interactions will be studied using a variety of techniques including affinity pull-down assays, gel filtration, and fluorescence polarization (FP). In addition, the role of TrpRS in selective packaging will be closely examined through the development of mutant forms of tRNATrp and TrpRS, and analysis of their effects on tRNA packaging in vivo. The insights gained from the proposed research may be useful in the design of therapeutic agents that target avian retroviruses. [unreadable] [unreadable]